It is widely assumed that human activities are affecting world climate and that scientists have a clear understanding of this phenomenon, based on comprehensive and trustworthy data. Unfortunately, the truth of the matter is the scientific understanding of climate change is not at all as comprehensive as is commonly assumed.
The atmosphere is an extremely complex system and attempts to model its behaviour make dullards of our fastest super-computers. Also, a model is only as good as its power to explain and predict climate change. You know a model is good if it can accurately reproduce, when fed with appropriate data, climate changes known to have occurred over a period.
Comprehensive data on changing atmospheric composition (i.e. gases and particles) and changing weather indices such as temperature, rainfall, windiness, cloud cover, etc. is required in order to test models. This data collection is currently inadequate and, therefore, the nations of the world must commit to long-term climate monitoring now.
The world certainly does appear to be warming up and the principal mechanism proposed to explain this warming is a strengthening of the greenhouse effect. The only external heat received by the earth comes from the sun. This heat warms the earth but the heat would be radiated back into space were it not trapped close to the earth by the insulating effect of certain gases in our atmosphere, principally carbon dioxide.
This is the greenhouse effect. The greater the concentration of insulating gases in the atmosphere, the greater the effect and the warmer the earth.
The burning of fossil fuels (coal, oil, gas, peat) releases carbon dioxide into the atmosphere. Fossil fuel emissions have raised carbon dioxide levels in the atmosphere by about 30 per cent since the beginning of the Industrial Revolution, around 1800.
The inevitable result is global warming. Most scientists agree the average temperature of the earth has risen by at least 0.6 degrees over the past 120 years, largely due to the burning of fossil fuel. Global warming dries the earth by evaporating more water from the seas, soil and plants. The additional water in the atmosphere is bled by all precipitating weather systems, i.e. tropical storms, thunder showers, snowstorms and frontal systems, thereby enhancing the global water cycle.
This leads to more severe droughts in dry areas and heavier rainfall or snowfall in wet areas. Such weather patterns have been noted in many parts of the world in recent decades.
I have noticed the changing weather patterns locally over the past 20 years since I first moved to the elevated area where I now live. For the first few years, road conditions on the local hill were dangerously icy for about six weeks each winter. Each of these early years was also marked by at least one week of heavy snow. But for the last 15 years, the hill has been ice-free and we never get more than the lightest flurry of snow anymore. The winter has generally became warmer and wetter.
Although we have a general idea of why the world is warming up, we are still unable to predict specifically how human activity in any particular place will affect the local and the global climate. In order to do that, much more accurate climate models will have to be constructed and this will require super-computers that run a million times faster than current models.
These models must be able to accurately simulate past and current climate change before we can rely on them to predict the future. Such models can only be constructed with the aid of an ongoing comprehensive record of changes as they occur.
Computer power is now increasing at such a rate that it will have improved one million-fold in 30-40 years. These powerful computers will allow much better models to be built. In order to test the models, accurate climate and atmospheric composition data, both historic and current, are needed.
To understand climate dating back to times before weather-tracking satellite etc, indicators such as air bubbles and chemicals trapped in ice cores, width of tree rings, coral growth, etc, are used. To understand the present climate, much more detailed observations are required on a continual basis, for example, measurement of extent of sea-ice, snow cover, soil moisture, ocean temperature, vegetative cover, etc.
One major problem is no international body has the mandate or resources to monitor longterm climate. Scientists now collect their data on climate change from miscellaneous sources such as satellites, ships, observatories, weather stations and aeroplanes which are primarily operated for other purposes, such as short-term weather forecasting. Consequently, our picture of climate variability is often patchy or equivocal.
Because current climate models are relatively insensitive and of poor predictive power, a large degree of uncertainty regarding the human impact on climate remains.
This uncertainty allows vested interests to argue against the introduction of legislation to curb fossil-fuel emissions. This leads to slow progress in changing standards in these areas.
We urgently need to know the precise effect of human activities on climate. Of its nature, acquiring this knowledge calls for the building of new improved climate models which is a slow process, but there is no other way.
We could know the answer within 50 years, but only if the nations of the world commit to long-term climate monitoring now.
A comprehensive account of this subject is presented in an article by T.R. Karl and K.E. Trenberth in the December 1999 issue of Scientific American.
(William Reville is a senior lecturer in biochemistry and director of microscopy at UCC.)